Attention has been drawn to the deleterious effect of ultraviolet radiation on the skin in recent years. It is now recognized that exposure of the skin to excess ultraviolet radiation is harmful to health and beauty, because ultraviolet radiation not only causes wrinkles, but also invites pigmentation and skin aging to appear as freckles and spots and even induces skin cancers. To protect the skin from harmful ultraviolet radiation, a number of cosmetics having UV absorbers blended therein are now marketed.
There are known many UV which are useful in this application, including benzotriazole derivatives such as 2-(2-hydroxy-5-methylphenyl)benzotriazole, benzophenone derivatives such as 2-hydroxy-4-methoxybenzophenone, cinnamic acid derivatives such as 2-ethoxyethyl 4-methoxycinnamate, p-aminobenzoic acid derivatives, and salicylic acid derivatives. These UV absorbers, however, have problems including percutaneous absorption, skin irritation, solubility, and limited contents.
Inorganic pigments such as titanium oxide, zinc oxide and iron oxide, are also known as UV shielding agents to be blended in cosmetic compositions. Since these agents provide UV protection by scattering UV light rather than absorbing, their UV protection is insufficient. They shield visible light. They also have problems of skin irritation and toxicity.
Further, organopolysilanes having a silicon-to-silicon bond are known to be UV absorptive. Particularly for dimethylpolysilanes, it was reported that the longer the silicon chain to the longer wavelength side the absorption band is shifted. Most well-known dimethylpolysilanes have UV absorption bands at shorter wavelengths than 250 nm, but can not sufficiently absorb UV in the wavelength range of 290 nm or higher, which is believed to be harmful to the skin. Increasing the silicon chain results in a reduced solubility in organic solvents, a reduced blending in cosmetic compositions, and thus limited utilization.
The present invention is made to eliminate the above mentioned drawbacks, and its primary object is to provide a novel and improved UV absorber which is effective in absorbing UV rays having a wavelength of 290 nm or higher, less susceptible to percutaneous absorption, less irritative to the skin, and having the least amount of toxic.